Reflective data storage medium made by silver diffusion transfer in silver-halide emulsion incorporating nuclei

ABSTRACT

A reflective laser recording and data storage medium, for direct reading after writing, formed from a photosensitive silver-halide emulsion including silver precipitating nuclei. A single step negative silver diffusion transfer process is used to develop silver nuclei of the latent image and dissolve unexposed silver halide elsewhere, forming silver ion complexes. These complexes are transported by diffusion transfer to the developing silver nuclei sites where silver is precipitated and adsorbed to form a high concentration of non-filamentary particles at a surface of a low melting temperature dielectric matrix which is highly reflective of light and electrically non-conducting.

CROSS REFERENCE TO RELATED APPLICATION

This application is a division of application Ser. No. 55,270, filedJuly 6, 1979 by Eric W. Bouldin and Jerome Drexler.

BACKGROUND OF THE INVENTION

a. Field of the Invention

The invention relates to laser recording media, and more particularly toa reflective silver data recording and storage medium useful for readinglaser recordings immediately after laser writing which is made from asilver-halide photosensitive emulsion by diffusion transfer.

b. Prior Art

Previously, many types of optical recording media have been developedfor laser writing. For example, an article in Optical Engineering, Vol.15, No. 2, March-April, 1976, p. 99 discusses properties of a largenumber of media. Some of these media require post write processingbefore they can be read, and some can be read immediately after laserwriting. The media of interest herein are for "direct read after write"capability, commonly known as "DRAW" media. Presently known laser DRAWmedia are thin metal films in which holes may be melted, composite shinyfilms whose reflectivity at a spot may be reduced by evaporation, thinfilms of dyes or other coatings which can be ablated at a spot, anddielectric materials whose refractive-index may be changed at a point,causing a scattering of light when scanned with a read laser.

The most common DRAW media are thin metal films, usually on a glasssubstrate. Thin metal films have several advantages: First, they can beproduced easily in small quantities with commercially availablesputtering equipment. Second, they can be read either by reflection orby transmission. Third, films of tellurium and bismuth have relativelyhigh recording sensitivities.

Fortunately, for all of these reasons, metal films have enabled a largeamount of research to be conducted and progress to be made in the designof optical data storage systems. To date, tellurium must be manufacturedby an expensive, batch-type, vacuum sputtering technique, it does notform a tenacious coating; and it introduces manufacturing andenvironmental complications because of its toxicity and since it rapidlyoxidizes in air it must be encapsulated in an airtight system in orderfor it to achieve an acceptable archival life.

What is particularly desirable about tellurium is that it has a lowmelting temperature for a metal, 450° C., and also a very low thermalconductivity of 2.4 watts per meter per degree Kelvin at 573° K. Incomparison, silver metal has a melting temperature of 960° C. and athermal conductivity of 407 watts per meter per degree Kelvin at thesame elevated temperature. When these two metals are considered forlaser recording with short pulses of laser power, the tellurium is farsuperior from a recording sensitivity standpoint since the low thermalconductivity keeps the heat generated by the laser beam confined to asmall area and the lower melting temperature facilitates the melting ofthe hole. Conversely, silver metal, because of its high thermalconductivity, about 170 times that of tellurium, would not normally beconsidered suitable for laser recording.

Attempts have been made to improve the laser recording sensitivity ofvarious types of metal layers. In U.S. Pat. No. 3,911,444 Lou, Watsonand Willens disclose a vacuum-deposited metal film recording media forlaser writing incorporating a separately deposited plastic filmundercoat between the metal film and a flexible transparent substrate tothermally insulate the metal layer in order to require less energy towrite with a laser.

Although it is possible to produce reflective metallic coatings of manytypes of substrates by vacuum sputtering or evaporation, silver isrelatively unique in that it can also be created by photographictechniques and, in particular, by silver diffusion transfer. In U.S.Pat. No. 3,464,822 Blake discloses a silver diffusion transfer reversalprocess for creating electrically conducting silver images for thefabrication of printed circuit boards. That invention, in turn, is basedupon silver diffusion transfer process inventions of the reversal type,leading to black non-reflective and non-conductive images, one examplebeing U.S. Pat. No. 2,500,421 by Dr. E. H. Land. The silver diffusiontransfer reversal process forms the basis of direct positives by thePolaroid Land process of Polaroid Corporation and the Gevacopy andCopyrapid processes of Agfa-Gevaert. These reversal processes should bedistinguished from the silver diffusion negative process. One suchprocess leading to black non-reflecting and non-conducting images, isdescribed in U.S. Pat. No. 3,179,517 by Tregillus. A silver diffusiontransfer negative process is used in the present invention.

It is well known that if very small, high electrical conductivity metalspheres or spherical particles are distributed through a dielectricmedium, the effective dielectric constant or refractive index will riseowing to the added induced dipoles of the metal particles. For the caseof homogeneously distributed particles, see Principles of MicrowaveCircuits, edited by C. G. Montgomery, McGraw Hill Book Company, Inc.,1948, pp. 376-397.

Previously, a reflective silver laser recording medium was the subjectof a prior patent application Ser. No. 012,235 by J. Drexler. In thatapplication, a processed black silver emulsion was converted to areflective recording medium by heating at least to 250° C. until a shinyreflective appearance is achieved.

An object of the invention was to devise a non-toxic, reflective DRAWlaser recording and data storage medium which may be manufacturedwithout the use of a vacuum system and on a continuous basis and whichmay be used to record low-reflective spots in a reflective field withrelatively low energy laser pulses. Another object was to devise areflective laser recording and data storage medium which permits thepre-recording of control indicia and certain data base data byphotographic means to facilitate the use of discs or plates in both therecording apparatus and the playback apparatus. Another object was topermit replication of optically recorded media by photographic contactprinting on a rigid flexible substrate that can be read in reflection ortransmission. Another object was to devise a laser recording and datastorage medium which could be fabricated from commercially availablephotoplates and films or minor modifications thereto, to achieve lowcost. Another object was to devise a laser recording medium which doesnot require a high temperature processing step and therefore will permitthe use of ordinary, low-cost photographic plastic film bases or otheravailable plastics as substrate materials permitting fabrication ofrecording discs with center holes by a low-cost stamping operation. Yetanother object of this invention was to devise a single-step silverdiffusion transfer photographic process which could produce a highlyreflective electrically non-conducting surface layer having a thicknessof 1 micron or less contained almost entirely within the gelatin orcolloidal carrier.

SUMMARY OF THE INVENTION

The above objects have been met with the discovery that the silver in aphotosensitive, silver-halide emulsion of a photoplate or film having anuclei layer therein can be brought to a surface of the emulsion to forma reflective laser recording and storage medium by a novel single stepsilver diffusion transfer negative photographic process. The nucleilayer should precipitate silver and have a gradient of decreasingconcentration in the depthwise direction. The present invention involvesa single step monobath silver diffusion transfer development process forthe emulsion that is primarily a solution physical development processwhich is used to build up the volume concentration of silver at thesurface containing the precipitating nuclei until the surface becomesreflective.

This reflective surface layer is typically less than one micron thick;has a reflectivity of 15% to 50%; is electrically a non-conductor andthermally a poor conductor since the matrix is typically gelatin, whichholds the high concentration of tiny particles and agglomerates ofsilver particles which are separated and isolated from each other by thegelatin matrix. Thus, although the layer reflects light like a metal, itmelts easily like a plastic, with the result that its recordingsensitivity is in the class of bismuth and tellurium and at least anorder of magnitude more sensitive than that of a thin, continuous silvermetal layer.

The nuclei always have a concentration which is greatest at the onesurface of the emulsion and least in the interior of the emulsion. Thesurface of greatest concentration may be either the surface distal tothe substrate or proximate thereto, depending on where laser writingwill initially impinge on the medium. For example, if laser writing ison the upper surface, the emulsion surface distal to the substrate hasthe greatest concentration of exposed silver halide. During the originalmanufacture of the silver-halide photographic plate or film a very thingelatin layer containing silver-precipitating nuclei would be includedat the surface distal to or the surface proximate to the substrate,which would be the basis for creating a reflective surface at either ofthese two surfaces.

The principal step of the process involves contacting the exposed oractivated and unexposed silver halide with a monobath containing asilver-halide developing agent for physically developing the nuclei. Asilver-halide solvent in the monobath, preferably a soluble thiocyanateor ammonium hydroxide, reacts rapidly with unexposed and undevelopedsilver-halide to form soluble complexed silver ions which aretransported by diffusion transfer to the nuclei, where the silver in thecomplexed silver ions is precipitated in the presence of the silverhalide developing agent. This process forms a reflective silver image.Recording is accomplished by puncturing through the reflective componentwith a laser beam so as to create a hole in the reflective componentwhich may later be detected by a variety of means such as reducedreflection of the hole; scattering of light from the hole; increasedlight transmission through the hole; and, if the recording is done onthe surface distal to the substrate, detection may be accomplished bymeans of mechanically probing the surface relief image of the hole.

An advantage of the above method for making a reflective recordingmedium is that it allows a low-cost manufacturing process to create aprecise very thin patterned reflective silver layer on the medium whichcould be used for laser recording without resorting to high-temperatureprocesses which could limit the selection of substrate materials.Several embodiments of the present method may be carried out bycontinuous manufacturing operations, as opposed to batch operations, butbatch procedures may also be used.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view of the recording medium of the presentinvention.

FIG. 2 is a side sectional view of the recording medium of FIG. 1, takenalong lines 2--2.

FIGS. 3-8 are detail views of the recording medium of FIG. 1 showing theresults of different combinations of photographic processing steps formaking the finished recording medium.

FIGS. 9-11 are side sectional views of three versions of the recordingmedium of FIG. 1 showing methods of laser reading or writing.

FIG. 12 is a plot of relative contrast ratio versus laser power for twomaterials.

FIG. 13 is a plot of percent reflectivity versus exposure for twomaterials.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The reflective laser recording medium of the present invention is madein one principal step involving silver diffusion transfer.

I. Surface Latent Image Formation

During the original manufacture of the silver-halide photographic plateor film a very thin gelatin layer containing silver-precipitating nucleiwould be included at the surface distal to or the surface proximate tothe substrate, which would be the basis for creating a reflectivesurface at either of these two surfaces. To record control indicia onthe medium, part of the emulsion may be masked or alternatively may havebeen exposed and chemically developed black. Typically such a medium isa disk, as illustrated in FIG. 1; however it could be a plate or filmstrip.

FIG. 1 shows a disc 11 having an inner periphery 13 and an outerperiphery 15. The interior of the inner periphery 13 is void so that acentering collar may be used to hold disc 11 on a spindle for high speedrotation. While the recording medium of the present invention isdescribed as a disc, a disc configuration is not essential for operatingof the recording medium. For example, the recording medium may be a flatsheet-like material which could be square and with a central hub ratherthan a hole. It could also be a non-rotating rectangular plate. However,rotating discs are preferred for fast random access to medium amounts ofdata and non-rotating rectangular plates in stacks are preferred toprovide intermediate speed random access to large amounts of data bymechanically selecting a plate and scanning it by mechanical andelectro-optical means.

The disc of FIG. 1 is photographically partitioned into recording andnon-recording areas. For example, a first annular recording zone 17could be spaced from a second annular recording zone 19 by an annularguard zone 21. The function of the guard zone may be to separatedifferent recording fields, to carry control information, such as timingsignals and to provide space for data read-write transducers to residewhen not over recording areas. While such guard bands are preferable,they are not essential to the operation of the present invention. Itshould be noted that the recording fields are for data and controlsignal recording, while the guard band is not for data recording, butmay have control signal recording thereon. The recording field 19 isshown to have a plurality of concentric, circumferentially-spaced servoguides 23 thereon. Such servo guides are thin lines which define thespaces between circular paths wherein data are written. The pattern forsuch lines is applied photographically as explained below with referenceto FIGS. 3-8.

FIG. 2 shows a side sectional view of the recording medium of FIG. 1.The medium consists of a substrate 27 which is a sheet-like layer whichmay be transparent or translucent, preferably a dimensionally stablematerial, like glass or plastics used for photographic film bases.Opaque, light-absorptive materials will work in those applications ofthe present invention where light transmission through the substrate isnot desired. Transparency or absorptivity of the substrate is desired sothat when the light beam of the reflective playback apparatus impingesupon a recorded spot, it either passes through the substrate or isabsorbed by it with minimum reflection. If the substrate is absorptive,it may be absorptive at the wavelengths of the recording beam or thereading beam, or preferably both. The most common photographic filmbases are polyester polyterephthalate, polycarbonate, or cellulosetriacetate.

For the case where the substrate is transparent and not birefringent,recording and reflective reading of the data can be done through thesubstrate as shown in FIGS. 10 and 11, or from the side distal to thesubstrate as shown in FIG. 9. For transmissive read, the configurationsof FIGS. 10 and 11 may be used. If the substrate is absorptive thenreflective read is the only possibility and the configuration of FIG. 9would be used.

The thickness of the substrate is not critical when the laser beam isdirected onto the surface as shown in FIG. 9, but it should havesufficient thickness to provide strength for resistance againstbreakage. If the laser beam is directed through a transparent substrate,as in FIGS. 10 and 11, then in order to maintain focus of the beam thethickness of the transparent substrate would have to be very uniform(for example, as obtainable from float glass or selected high qualitydrawn glass). Also, the thickness of the substrate may depend on theoverall size of the recording medium being used. For a 12-inch disc, athickness of 1/8 inch may be suitable.

The purpose of substrate 27 is to support a silver-halide emulsioncoating 29, which is uniformly applied to the substrate in aconventional manner and which is converted by silver diffusion transferinto components 32 and 33 in FIGS. 9, 10 and 11. This process forcreating the reflective layer 32 does not require any chemicalconstituent within the emulsion other than a conventional silver halideheld in a suitable colloid carrier, preferably gelatin. They may alsocontain optical and chemical sensitizers, anti-fogging agents,stabilizing compounds, emulsion hardeners and wetting agents. However,when commercial photoplates or films are used, they may contain certainphysical characteristics or added chemical ingredients which could leadto favorable or unfavorable results. For example, most photographicfilms have a gelatin overcoat over the silver-halide emulsion that mighthave a thickness of 1 micron. Since layer 32 is not electricallyconducting but reflects owing to its high dielectric constant, anymoderately thick, high dielectric constant coating over it will reduceits reflectivity.

One of the advantages of gelatin is that it has a relatively low meltingtemperature, less than 400° C., which aids laser recording. Such lowmelting temperature carriers are preferred in the present invention.

Emulsion thicknesses of 3 to 6 microns are adequate to containsufficient silver-halide emulsion to build up the reflective layer bythe complexing and diffusion transfer steps. If thicker commercialemulsions are used along with long processing times, the reflectivelayer may become too thick or too thermally conducting to permitrecording with low-power lasers. The thicker coating requires a higherlaser beam power to penetrate it and a higher thermal conductivity leadsto faster heat flow away from the spot being recorded, also leading tohigher recording powers.

If a hardened emulsion is desired it may be preferable to harden orcross link the gelatin after forming reflective layer 32. If theemulsion is hardened initially, then it will swell to a reduced extentduring monobath processing thereby reducing the rate at which the silverhalide is dissolved and complexed, thus extending the process time.

Small silver-halide grains typically found in commercially availablehigh resolution or high definition photoplates used in photomask making,holography and high-resolution recording are excellent for producingreflective laser-recording materials. These emulsions typically havemean grain sizes of 0.05 micron and a spread of about 0.007 micron. Onetype, the Agfa-Gevaert Millimask HD photoplate, has a mean grain size of0.035 micron and a spread of 0.0063 micron. The finer grains result inminimizing the micro variations or granularity in reflectivity andthickness of the reflective component and thereby permit recording andreading of smaller holes than for coarse grain emulsions. The finergrain emulsions also dissolve faster owing to their greatersurface-to-volume ratio which leads to a shorter process time.

High resolution emulsion coated glass plates having thesecharacteristics are commercially available and are known as photoplateswhich are used to make photomasks for the manufacture of semiconductorintegrated circuits. For example, emulsion coated photoplates suitablefor use herein are manufactured by Agfa-Gevaert of Belgium, KonishirokuPhoto Industries Co., Ltd. of Japan and the Eastman Kodak Company.However these commercial products do not contain silver precipitatingnuclei and any of these products could be converted during the emulsioncoating processes.

The shiny reflective component 32 in FIGS. 9, 10 and 11 result from thephotographic monobath processing described herein but the silver ispresent initially as silver halide and reflectivity does not initiallyexist in the emulsion. Thus at the inception the silver of reflectivecomponent 32 is found in the photographic emulsion 29, which is uniformin its composition. An inert subbing layer, not shown, is usually usedto attach the substrate 27 to the emulsion 29. Following thephotographic conversion of the present invention the emulsion 29 of FIG.2 produces a reflective component 32 at the emulsion surface shown inFIG. 9, with a low-reflective underlayer 33 beneath it. The reflectivelayer 32 is sharply defined in thickness due to nuclei being includedduring manufacturing.

If any light exposure occurs in underlayer 33, prior to chemicalprocessing, the underlayer, while not completely depleted of silver,contains much less silver than reflective component 32. Optically,underlayer 33 is either clear or reddish in color which is transmissiveto red light having wavelengths of 630 nanometers and longer. Underlayer33 tends to be clear or slightly yellow if the silver-halide therein isnot subject to light exposure. Underlayer 33 tends to be amber or red iflight exposure occurs in the underlayer.

Owing to the dielectric constant of the glass a higher volumeconcentration of silver is necessary to give the same reflectivity ascompared to an emulsion side reflective layer. The required layer ofhigh concentration silver precipitating nuclei at the substrate ordistal to the substrate can also be incorporated during the film orphotoplate manufacturing process.

Once craters are created penetrating reflective component 32, the datacontained in the craters may be read by changes in reflectivity of theshiny reflective component throughout the visible spectrum and into thenear infrared where it is ultimately limited in its usability asreflective component 32 becomes more and more transparent and thereforeless reflective. The craters also may be detected by transmission of redlight, provided that the opacity of the reflective layer is sufficientlygreat at the selected wavelength to permit detection of the cratersthrough differences in light transmission.

It should be noted that both the recording areas 17, 19 and thenon-recording guard band 21 of FIG. 1 initially have silver-halideemulsion covering a substrate. Thus, the designation of recording andnon-recording areas is arbitrary and the entire surface could be usedfor recording if desired. However, as a matter of convenience, it ispreferable to designate areas as non-recording areas. The boundariesbetween recording and non-recording areas may be defined by concentriclines, just as the servo guides 23 of FIG. 1, which have been greatlyenlarged in the Figure, may be defined by lines. Typically, servo guidesare closely spaced concentric circles or adjacent lines of a spiral,with data being written on or between the lines. Such servo guide lines,as well as line boundaries for non-recording areas, may bephotographically recorded on the recording medium prior to any datarecording. Moreover, other alphanumeric information or data baseinformation which is to be a permanent part of the recording medium alsomay be applied to the recording medium photographically at an early timein the processing cycle since it becomes a permanent part of therecording medium.

One of the advantages of the present invention is that the permanentinformation to be pre-recorded on the recording medium of the presentinvention may be applied by photographic techniques since the startingmaterial for the recording medium is an unexposed commercially availablephotoplate used in the manufacture of semiconductor integrated circuitsor film-based materials of similar quality. A principal characteristicof silver-halide emulsion photosensitive materials for use in thepresent invention is fine grain size so that the reflectivitygranularity is minimized and very small holes can exhibit measurablechanges in reflectivity. Large grain sizes would lead to greatergranularity which would tend to mask changes in reflection created bysmall holes. Pre-recording of information may be achieved by masking offareas as described herein. After photographic processing, thispre-recorded information may be read in reflection since thepre-recording areas will consist of either highly reflective whitesilver areas or low reflective black silver areas or low reflectivityclear gelatin areas.

The photographic techniques which may be used to prerecord data base andcontrol information are closely related to the fabrication of emulsionphotomasks in the semiconductor industry. Lines having a thickness ofone micron may be made using these photomask manufacturing techniques.Some procedures for creating a pre-recorded line pattern are illustratedin FIGS. 3-8.

With reference to FIG. 3, fine grain silver-halide emulsion medium 11 isexposed to actinic radiation in the areas for non-data recording but theline pattern consisting of the circular lines 23a, 23b and 23c is maskedfrom the radiation. This procedure creates a surface latent imageformation in the non-data recording areas. The masked areas are thenunmasked and the emulsion is subjected to a standard chemicaldevelopment process to develop medium 11 black. Then the medium issubjected to the monobath processing described herein which creates areflective surface for laser recording on 23a, 23b, 23c in FIG. 4. Theblack area in this figure represents black silver and the white areasrepresent reflective silver.

There is a principal reason that the silver can be concentrated at thesurface distal to the substrate. When the emulsion is dipped into themonobath the surface silver precipitating nuclei are immediatelyavailable for solution physical development. Thus, when the solutionphysical development of the monobath begins, complexed silver ions willprecipitate on the surface where the silver precipitating nuclei arenumerous.

The circular lines 11 which were developed black represent lowreflectivity servo guides which would provide information as to whetherthe recording laser is recording on the data track or has moved off theedge of the data track. To provide additional information to the servosystem, the servo guides could contain a reflective and non-reflectivepattern shown in FIG. 5, which would provide information as to whetherthe correction requires a movement to the right or left. Note that theright and left servo guides would provide different frequency signals tothe playback system. The dashed pattern shown could be created in themaster by means of a photomask or by interrupting a laser photographicrecording beam.

For the servo guides or any other indicia markings to be in the form oflow reflective black silver, as opposed to clear gelatin markingsdiscussed above, the servo guides themselves could be exposed through amask or by means of a continuous or interrupted laser beam. FIG. 6illustrates the making of such indicia where actinic radiation is usedfirst to expose servo guides 43a, 43b, 43c and the remaining area 41would be shielded. Then a normal chemical or direct development would beused to create a black low reflectivity pattern as shown in FIG. 7. Nofixing would be used since the silver halide in region 41 would be usedin the subsequent monobath processing to create reflective areas. Alsonote that the lines 43a, 43b, and 43c could have been broken into apattern such as those shown in FIG. 5. With the track guides andpossibly other indicia recorded in black silver, the next step would beto expose the surface latent image in the remaining areas for laserrecording.

The commercially available instant photographic films of thePolaroid-Land photographic system have silver-precipitating nucleilayers in contact with the silver-halide emulsion. Note that the use ofsilver-precipitating nuclei layers incorporated in the emulsion does notpreclude the possibility of pre-recorded control indicia. The non-datarecording areas may be exposed first and chemically developed to lowreflectivity black silver and not fixed. The entire plate is then givena monobath development to create reflective data recording areas. Ifdesired, the black silver areas created by the initial exposure anddevelopment could be bleached out before monobath processing. Thereflective component 32 of FIGS. 9-11 is thus derived from the silver inthe silver-halide emulsion.

A commercially available photographic emulsion containing nuclei is thestarting material for creating the laser-recording medium in the presentinvention, and the finished product may be considered to be silverparticles in a gelatin dielectric matrix, the halide being removed inthe monobath processing.

To use the laser recording medium of the present invention, laser lightis focused on a spot on the reflective component either from the sidedistal to the substrate or through a transparent substrate. For laserrecording as opposed to data storage applications the reflectivity ofthe reflective layer preferably ranges between 15% and 50%; thus, theremaining percentage of incident radiation of 85% to 50% is eitherabsorbed by the reflective component or partly passes through it. Theabsorbed power distorts or melts the gelatin supporting the reflectivecomponent so as to reduce the reflectivity at the spot and create anadequate contrast in reflective reading of the recorded data. For datastorage applications, i.e., laser reading but not recording thereflectivity may be as high as possible and the thickness of thereflective layer is not critical. The reflective component 32 is locatedon the underlayer as shown in FIG. 9 and FIG. 11 and adjacent to thesubstrate as shown in FIG. 10. In all three cases a reflective readprocedure can be used--for example, as described in U.S. Pat. No.3,657,707. In the cases shown, the recording laser beam need only effectthe reflective component, and further penetration into component 33 isnot needed.

In FIG. 9, the substrate could be either transmissive or opaque ifreflective read is used, but must be transmissive to the read laser beamif transmissive read is used. The component 33 would be essentiallyclear gelatin if the emulsion had been manufactured with a silverprecipitating nuclei layer included. If component 33 is essentiallyclear gelatin it would permit transmissive reading of data.

FIG. 10 illustrates a configuration produced by use of an emulsion whichhas been manufactured with a silver precipitating nuclei layer included.Thus, component 33 is essentially clear gelatin and transmissive readcan be accomplished.

FIG. 11 illustrates a configuration where both the substrate and theunderlayer are transmissive to visible and near infrared radiation. Ithas the advantage that layer 32 can be coated with a non-optical flatprotective layer which would serve to encapsulate layer 32. This type ofprotective layer could not be used in the configuration of FIG. 9because it would be in the optical path. The configuration of FIG. 11also offers an advantage over the configuration of FIG. 10 in thathigher reflectivities are more easily attainable by use of the hereindescribed process. The essentially clear gelatin component 33 can beproduced by use of an emulsion which had been manufactured with a silverprecipitating nuclei layer included at the location of layer 32. In thiscase in addition to reflective read at visible wavelengths and nearinfrared, the component 33 also permits transmissive read at thesewavelengths by laser light traversing substrate 27 for transmissionthrough the essentially clear gelatin component 33 and through crater 30in component 32.

FIGS. 9, 10 and 11 show emulsion coating 29 on substrate 27 covered byshiny component 32 having a crater 30 damaging the shiny componentcreated by means of laser light indicated by the rays 31. The size ofthe craters is kept at a minimum, preferably about one micron indiameter but no larger than a few microns in diameter to achieve highdata densities. Data written by means of laser light are recorded in therecording areas 17, 19 shown in FIG. 1, designated by the letter R. Asmentioned previously, these recording areas may also containpre-recorded data base data and control indicia which may be disposedover essentially the entire area of the medium. No data is recorded inthe guard band 21, designated by the letter G, although this region mayhave control indicia written therein. Control indicia in either of theareas may be written by means of photographic techniques or bypyrographic methods such as laser writing.

Thus, the recording medium of the present invention may contain a mix ofpre-recorded data and control indicia which has been applied to therecording medium by photographic techniques, as well as subsequentlywritten data applied to the recording medium by laser pyrographicwriting. There need be no data storage distinction between thephotographically pre-recorded non-reflective spots and non-reflectivespots made by laser writing. In the recording mode the pre-recordedcontrol information is used to determine the location of the datacraters being recorded.

II. Silver Diffusion Transfer

We have found that a very thin, highly reflective, silver surface may beformed by the diffusion transfer of appropriate complexed silver ions toa layer of silver precipitating nuclei. This reflective layer iselectrically non-conducting and has low thermal conductivity and may bepatterned photographically, these latter two properties being highlydesirable for laser recording media. The complexed silver ions arecreated by reaction of an appropriate chemical and the silver halideused in conventional silver-halide emulsions. A developing or reducingagent must be included in this solution to permit the complexed silverions to be precipitated on the nuclei layer. This combination ofdeveloping agent and silver complexing solvent in one solution is calleda monobath solution. Preferred monobath formulations for highlyreflective surfaces include a developing agent which may becharacterized as having low activity. The specific type of developingagent selected appears to be less critical than the activity level asdetermined by developer concentration and pH.

The developing agent should have a redox potential sufficient forcausing silver ion reduction and adsorption or agglomeration on silvernuclei. The concentration of the developing agent and the pH of themonobath should not cause filamentary silver growth which gives a blacklow reflectivity appearance. The developed silver particles should havea geometric shape, such as a spherical or hexagonal shape which whenconcentrated form a good reflectivity surface.

Developing agents having the preferred characteristics are well known inthe art and almost any photographic developing agent can be made to workby selection of concentration, pH and silver complexing agent, such thatthere is no chemical reaction between the developing agent andcomplexing agent. It is well known that photographic developing agentsrequire an antioxidant to preserve them. The following developingagent/antioxidant combinations produced the typical indicatedreflectivities for exposed and monobath developed Agfa-Gevaert MillimaskHD photoplates.

    ______________________________________                                        For Monobaths Using Na(SCN) As a Solvent                                      And Silver Complexing Agent                                                                            Approximate                                          Developing Agent                                                                            Antioxidant                                                                              Maximum Reflectivity                                 ______________________________________                                        p-methylaminophenol                                                                         Ascorbic Acid                                                                            46%                                                  p-methylaminophenol                                                                         Sulfite    37%                                                  Ascorbic Acid --         10%                                                  p-Phenylenediamine                                                                          Ascorbic Acid                                                                            24%                                                  Hydroquinone  Sulfite    10%                                                  Catechol      Sulfite    60%                                                  ______________________________________                                        For Monobaths Using NH.sub.4 OH As a Solvent                                  And Silver Complexing Agent                                                   Developing Agent                                                                            Antioxidant                                                                              Typical Reflectivity                                 ______________________________________                                        Hydroquinone  Sulfite    25%                                                  Catechol      Sulfite    30%                                                  ______________________________________                                    

The preferred solvents/silver complexing agents, which must becompatible with the developing agent, are mixed therewith, inproportions promoting the complete diffusion transfer process withinreasonably short times, such as a few minutes. Such silver complexingagents in practical volume concentrations should be able to dissolveessentially all of the silver halide of a fine grain emulsion in just afew minutes. The solvent should not react with the developing silvergrains to dissolve them or to form silver sulfide since this tends tocreate non-reflective silver. The solvent should be such that thespecific rate of reduction of its silver complex at the silver nucleilayer is adequately fast even in the presence of developers of lowactivity, which are preferred to avoid the creation of low-reflectivityblack filamentary silver in the initial development of the surfacelatent image.

The following chemicals act as silver-halide solvents and silvercomplexing agents in solution physical development. They are groupedapproximately according to their rate of solution physical development;that is, the amount of silver deposited per unit time on precipitatingnuclei, when used with a p-methyl-aminophenol-ascorbic acid developingagent.

Most Active

Thiocyanates (ammonium, potassium, sodium, etc.)

Thiosulphates (ammonium, potassium, sodium, etc)

Ammonium hydroxide

Moderately Active

α picolinium--β phenylethyl bromide

Ethylenediamine

2-Aminophenol furane

n-Butylamine

2-Aminophenol thiophene

Isopropylamine

Much Less Active

Hydroxylamine sulfate

Potassium chloride

Potassium bromide

Triethylamine

Sodium sulfite

From the above it can be seen that the thiocyanates and ammoniumhydroxide are amongst the most active solvents/complexing agents. Whilealmost all developers suitable for solution physical development can bemade to work in the silver diffusion transfer process of the presentinvention with the proper concentration and pH, not allsolvents/complexing agents will work within the desired shortdevelopment time or in the proper manner. For example, the thiosulfatesalts, the most common silver-halide solvent used in photography inPolaroid-Land black and white instant photography's diffusion transferprocess, does not work in this process for two reasons. Its complexedsilver ions are so stable that it requires a strong reducing agent toprecipitate the silver on the nuclei, and this strong reducing ordeveloping agent would have the undesirable effect of developing lowreflective black filamentary silver. It has another undesirable effect,also exhibited by the solvent thiourea; namely, that it forms black, lowreflecting silver sulfide with the developing silver grains. On theother hand in the black and white Polaroid-Land process black silver isa desirable result. Sodium cyanide is not recommended, even though it isan excellent silver-halide solvent, because it is also an excellentsolvent of metallic silver and would thus etch away the forming image.It is also about 50 times as toxic as sodium thiocyanate, which is acommon photographic reagent.

The process chemicals can be applied by a variety of methods, such as byimmersion, doctor blades, capillary applicators, spin-spray processorsand the like. The amount of processing chemicals and temperature thereofshould be controlled to control reflectivity. Preferably, the molarweight of the developing agent is less than 7% of the molar weight ofthe solvent since higher concentrations of developing agent can lead tolow reflective filamentary silver growth, exceptions to this ratio beingfound among p-phenylenediamine and its N, N-dialkyl derivatives having ahalf-wave potential between 170 mv and 240 mv at a pH of 11.0, whichhave lower development rates and require higher concentrations, i.e., upto 15 grams per liter and minimum of about 2 grams per liter. Thesederivatives and their half-wave potentials are listed in Table 13.4 ofthe book entitled The Theory of the Photographic Process, 3rd ed.,Macmillan Company (1966). The concentration of the solvent in the formof a soluble thiocyanate or ammonium hydroxide should be more than 10grams per liter but less than 45 grams per liter. If the concentrationis too low the solvent would not be able to convert the halide to asilver complex within a short process time and if the solventconcentration is too great the latent image will not be adequatelydeveloped into the necessary silver precipitating nuclei causing much ofthe silver complex to stay in solution rather than be precipitated. Theprocess by which the silver complex is reduced at the silverprecipitating nuclei and builds up the size of the nuclei is calledsolution physical development.

It is important to note that in solution physical development, as usedherein, the silver particles do not grow as filamentary silver as indirect or chemical development, but instead grow roughly equally in alldirections, resulting in a developed image composed of compact, roundedparticles. As the particles grow, a transition to a hexagonal form isoften observed. If the emulsion being developed has an extremely highdensity of silver nuclei to build upon and there is sufficientsilver-halide material to be dissolved, then eventually the spheres willgrow until some contact other spheres forming aggregates of severalspheres or hexagons. As this process takes place the light transmittedthrough this medium initially takes on a yellowish appearance when thegrains are very small. This changes to a red appearance as the particlesbuild up in size and eventually will take on a metallic-likereflectivity as the aggregates form.

In summary, it was discovered that if silver precipitating nuclei areformed on one of the surfaces of a silver-halide emulsion either in theemulsion manufacturing process, and if this emulsion is then developedin a monobath solution containing a weak developer and a very fastsolvent which forms complexed silver ions which are readily precipitatedby catalytic action of silver nuclei; and if the solvent does not formsilver sulfide; then a reflective coating is developed on one of theemulsion surfaces thereby creating a medium for data storage and laserrecording. It was also discovered that any of the common developingagents will work whereas only a small number of solvents/complexingagents have all of the desired properties, the most successful of thesebeing the soluble thiocyanates and ammonium hydroxide.

In a common version of the black and white silver diffusion transferprocess the silver in the unused halide in the negative image willdiffuse to a second separatable layer containing precipitating nucleifor reducing the silver and thereby creating a positive image. In thediffusion transfer process of this invention, a volume concentration ofsilver precipitating nuclei are located on an emulsion surface withoutuse of a separate layer containing nuclei. The developing agent-solventmonobath performs two functions; it dissolves the silver halide withinthe body, creates complexed silver ions and provides the reducing agentnecessary for the solution physical development process, that is, thereduction and precipitation of the complexed silver ions on the silverprecipitating nuclei.

Thus, the key steps in the present invention involve adding a layer ofsilver-precipitating nuclei to the emulsion during the manufacturingprocess and then using a special monobath containing a developing agentand complexing agent to build up the silver grains of the silverprecipitating nuclei until they begin to aggregate into groups therebyincreasing the volume concentration of the silver in the surface latentimage area until it becomes adequately reflective. An alternativeprocedure is to use a silver-halide emulsion which is coated on one sideby, or otherwise incorporates a layer of, silver precipitating nucleiwhich is then exposed to light in the non-data-recording areas assignedto control indicia. This is then followed by a chemical development toproduce black control indicia or other pre-recordings and finally amonobath development of the special type previously described is used tobuild up the silver grains in the data recording area until it becomesadequately reflective. The resulting reflective laser-recording and datastorage medium consists of concentrated reflective silver grains near asurface of an essentially clear gelatin matrix.

Some of the key processing steps of the present invention may beachieved by physical phenomenon, chemical treatments or manufacturingtechniques but when these steps are linked together in the properprocessing sequence, the result is a reflective laser-recording medium.Table I presents 14 experimental examples to illustrate some of thevariations of the individual steps that may be used and to present anoverview of two principal steps necessary to create a laser recordingmedia of adequate reflectivity. In these examples actinic radiation or asurface fogging chemical were used to create silver precipitatingnuclei.

See Table I which follows.

                                      TABLE I                                     __________________________________________________________________________                                                             Typical              Example                                                                              Surface Activation                                                                      Developing Agent                                                                          Solvent/Complexing Agent                                                                    Photographic                                                                                Reflectivity         __________________________________________________________________________                                               Agfa HD Photoplate;*               Example 1                                                                            Light     P-Phenylendiamine                                                                         Sodium Thiocyanate                                                                          41/2 Micron Emulsion                                                                        20%-24%                               P-Methylaminophenol       Agfa HD Photoplate;                Example 2                                                                            Light     and Ascorbic Acid                                                                         Sodium Thiocyanate                                                                          41/2 Micron Emulsion                                                                        20%-35%                               P-Methylaminophenol       Konishiroku ST Photo-              Example 3                                                                            Light     and Ascorbic Acid                                                                         Sodium Thiocyanate                                                                          plate; 3 Micron                                                                             15%-27%n                              P-Methylaminophenol       Agfa-Gevaert Type 10E75            Example 4                                                                            Light     and Ascorbic Acid                                                                         Sodium Thiocyanate                                                                          film; 5 Micron                                                                              40%-43%n                    Aqueous Hydrazine                                                                       P-Methylaminophenol       Kodak S0173 Film;                  Example 5                                                                            Surface Fogging                                                                         and Ascorbic Acid                                                                         Sodium Thiocyanate                                                                          6 Micron Emulsion                                                                           32%                         Aqueous Hydrazine;                                                                      P-Methylaminophenol       Agfa HD photoplate;                Example 6                                                                            Surface Fogging                                                                         and Ascorbic Acid                                                                         Sodium Thiocyanate                                                                          41/2 Micron Emulsion                                                                        39%-41%                     Aqueous Hydrazine;                                                                      P-Methylaminophenol       Konishiroku SN Photo-              Example 7                                                                            Surface Fogging                                                                         and Ascorbic Acid                                                                         Sodium Thiocyanate                                                                          plate; 6 Micron                                                                             23%lsion                    Gaseous Hydrazine;                                                                      P-Methylaminophenol       Agfa HD Photoplate;                Example 8                                                                            Surface Fogging                                                                         and Ascorbic Acid                                                                         Sodium Thiocyanate                                                                          41/2 Micron Emulsion                                                                        22%                         Aqueous Potassium                                                                       P-Methylaminophenol       Agfa HD Photoplate;                Example 9                                                                            Borohydride;                                                                            and Ascorbic Acid                                                                         Sodium Thiocyanate                                                                          41/2 Micron Emulsion                                                                        75%                         Surface Fogging                                                                         P-Methylaminophenol                                                                       Hydroxylamine Agfa HD Photoplate;                Example 10                                                                           Light     and Ascorbic Acid                                                                         Hydrochloride 41/2 Micron Emulsion                                                                        18%                                   Catechol                  Agfa HD Photoplate;                Example 11                                                                           Light     1 gms./liter                                                                              Sodium Thiocyanate                                                                          41/2 Micron Emulsion                                                                        56%                                   Catechol                  Agfa HD Photoplate;                Example 12                                                                           Light-Micron Image                                                                      1/2 gm./liter                                                                             Sodium Thiocyanate                                                                          41/2 Micron Emulsion                                                                        35%                                   Catechol                  Agfa HD Photoplate;                Example 13                                                                           Light     1/2 gm./liter                                                                             Ammonium Hydroxide                                                                          41/2 Micron Emulsion                                                                        30%                                   Hydroquinone              Agfa HD Photoplate;                Example 14                                                                           Light     1/2 gm./liter                                                                             Ammonium Hydroxide                                                                          41/2 Micron Emulsion                                                                        25%                  __________________________________________________________________________     *Agfa HD is an abbreviation for AgfaGevaert Millimask HD Photoplate.     

In the following fourteen examples creation of nuclei in surface latentimages was achieved by actinic radiation, aqueous and gaseous fogging byhydrazine and aqueous fogging by potassium borohydride. The nucleiformed in this manner are analogous to a nuclei layer added in themanufacture of the emulsion. As previously mentioned, if a nuclei layeris already present and pre-recordings are desired, then surface latentimages must be created in the non-data recording areas. It appears thatany silver halide emulsion may be used to create a reflective silversurface. This invention is not limited to the use of gelatin-basedemulsions. Other film-forming colloids may be used as carriers. Avariety of commercially available high-resolution films and platesmanufactured by three different companies were used to illustrate thegeneral nature of the process. It is also shown that the monobathdeveloping-agent-complexing agent can be formulated by use of a varietyof developing agents and solvents/silver complexing agents. Table Ilists four different developing agents, three differentsolvents/complexing agents, five different emulsions and four differentsurface activation procedures. The reflectivities achieved range between15% and 75%.

EXAMPLE 1

A photoplate coated with a commercial Agfa-Gevaert HD emulsion 4.5microns thick and containing a screening dye was exposed to sunlight forseveral minutes and then immersed for five minutes at 23° C. in amonobath which contained the following formulation: p-phenylenediamine,5.4 grams; 1-ascorbic acid, 5.0 grams; KBr, 0.5 grams; and NaSCN, 10.0grams; with water added to bring volume up to 1 liter; and with a pH=11achieved by adding NaOH. After drying, samples exhibited a range ofreflectivities of 20% to 24% at 633 nanometers and a range of opticaldensities measured in the red with a commercial densitometer of 1.0 to1.2.

Laser recording was then accomplished with an argon laser using thegreen line at 514 nanometers. The beam diameter was approximately 0.8micron at the media surface, and pulse lengths of 100 nanoseconds wereused. Tests were conducted to determine how the reflective contrastratio varied with laser-beam power. Measurements were made starting atbeam powers of 28 milliwatts and down to under 5 milliwatts. The resultsof those tests for two samples are shown as curves "A" and "B" in FIG.12. The ratio of reflected power from the unrecorded surface to that ofthe hole at 24 milliwatts was in the range of 7:1 or 8:1. At eachmeasured power level, the contrast was measured at 32 points andaveraged.

EXAMPLE 2

A photoplate coated with a commercial Agfa-Gevaert Millimask HD emulsion4.5 microns thick and containing a screening dye was exposed in anexposure box through a stepped wedge stepped in optical density units of0.1 to produce ten exposure levels. Four sequential exposures were used,after which the plate was developed for five minutes at 23° C. in amonobath consisting of p-methylaminophenol sulfate, 0.28 grams;1-ascorbic acid, 2.8 grams; KB_(R), 1.0 grams; NaOH, 2 grams; NaSCN,22.0 grams; in a volume of 1 liter after adding water. The pH was 11.After drying, the reflectivity measured at 633 nanometers as a functionof log exposure is shown in FIG. 13 as curve "C".

EXAMPLE 3

A photoplate coated with a commercial Konishiroku ST emulsion 3 micronsthick containing no screening dye and with the backing removed wasexposed in an exposure box through a stepped wedge stepped in opticaldensity units of 0.1 to produce ten exposure levels. Three plates wereused. The first plate was exposed to one flash of actinic radiation; thesecond, to four; and the third, to sixteen. The plates were thendeveloped in the monobath described in Example 2. The processing timewas 5 minutes at 23° C. After drying, the reflectivity measurements weremade on the ten reflective steps on each of the three plates at 633nanometers as a function of log exposure and are shown in FIG. 13 ascurve "D". The curve covers a much greater range of log exposure thancurve "C" because "D" interconnects the data taken from the three platessubject to different exposures, while "C" represents only one plate.

EXAMPLE 4

A strip of Agfa-Gevaert 10 E75 film was exposed to room light forseveral minutes, then developed in a monobath, as described in Example2, for 2 minutes at 23° C. After drying, it did not appear reflective.It was concluded that the gelatin overcoat was reducing the overallreflectivity. The strip was immersed in a 0.5% Protease WT solution at35° C. for 4 minutes. The reflectivity was in the range of 40% to 43%and the optical density in the red was 2.5 to 2.7. Protease WT is amixture of enzymes and is a trademark of GB Fermentation Industries,Inc., of West Germany.

EXAMPLE 5

A commercially available Eastman Kodak SO 173 film was etched with aProtease WT 0.5% solution for 5 minutes at 35° C. in a darkroom toremove the gelatin overcoat. The film was then immersed in a hydrazine68% aqueous solution for 2 seconds to create the developable surfacelatent image. It was then developed in a monobath as described inExample 2, for 5 minutes. After drying, it exhibited a reflectivity of32% and a red density of 1.9 to 2.0.

EXAMPLE 6

An unexposed commercially available Agfa-Gevaert Millimask HD photoplatewas dipped into a 68% aqueous solution of hydrazine for several secondsto create a developable surface latent image. It was then developed inmonobath as described in Example 2 for 5 minutes at 23° C. and thendried. Samples exhibited reflectivities ranging between 39% and 41% atthe emulsion surface and reflectivities of 17% to 18% when measuredthrough the glass substrate. The gelatin under the reflective silvercoating was so clear that the silver coating was visually reflectivethrough the glass substrate. Optical densities in the red ranged between0.8 and 1.0.

EXAMPLE 7

A commercially available photoplate manufactured by Konishiroku PhotoIndustries, of Japan, called a KR SN photoplate, has a 6-micron-thickemulsion which does not contain a screening dye but does contain ananti-halation backing coated on the back of the glass substrate. Thisphotoplate was dipped into a 68% aqueous solution of hydrazine for a fewseconds and then developed for 5 minutes at 23° C. in monobath asdescribed in Example 2 and then dried. It exhibited a reflectivity fromthe emulsion side of 23% and an optical density in the red of 1.5.

EXAMPLE 8

A commercially available Agfa-Gevaert Millimask HD photoplate had latentimages created on its surface by means of gaseous hydrazine. Thephotoplate was placed in a chamber which is exhausted of air down to 13mm of mercury, after which hydrazine is evaporated into the chamber. Thephotoplate is exposed to this gas for 10 minutes in darkness and thendeveloped in monobath, as described in Example 2, for 5 minutes at 23°C. After drying, the plate exhibited a reflectivity of 22% and anoptical density in the red of 2.0.

EXAMPLE 9

A commercially available Agfa-Gevaert Millimask HD photoplate having a4.5 micron thick emulsion and containing a screening dye was immersed ina water solution consisting of 5 grams/liter of potassium borohydride(KBH₄) for 2 seconds to fog the surface and create silver nuclei forsilver diffusion transfer. After it was washed well, the photoplate wasdeveloped in the monobath described in Example 2 for five minutes at 23°C. When washed and dried, the plate exhibited a reflectivity of 75%.

EXAMPLE 10

A commercially available Agfa-Gevaert Millimask HD photoplate having a4.5 micron thick emulsion and containing a screening dye was exposed toroom light for several minutes and then developed for 2 hours in amonobath developer having the following constituents:p-methylaminophenol sulfate, 0.25 grams; ascorbic acid, 2.5 grams;sodium hydroxide, 2.0 grams; hydroxylamine hydrochloride (H0--NH₂--HCL), 5 grams; in a volume of one liter after adding water. After thephotoplate was washed and dried, its reflectivity was measured at 18.5%.

EXAMPLE 11

A commercially available Agfa-Gevaert Millimask HD photoplate having a4.5 micron thick emulsion and containing a screening dye was exposed toroom light for several minutes and then immersed for five minutes at 23°C. in a monobath developer having the following constituents: catechol,1 gram; sodium sulfite, 10 grams; sodium hydroxide, 2 grams; sodiumthiocyanate, 25 grams; in a volume of one liter after adding water.After the photoplate was washed and dried, it exhibited a reflectivityof 56%.

EXAMPLE 12

A commercially available Agfa-Gevaert Milimask HD photoplate having a4.5 micron thick emulsion and containing a screening dye was exposedthrough a photomask containing one micron serpentine lines for 8 secondsusing an Ultratech contact printer and then immersed for five minutes at23° C. in a monobath developer having the following constituents:catechol, 1/2 gram; sodium sulfite, 10 grams; sodium hydroxide, 2 grams;sodium thiocyanate, 25 grams; in a volume of one liter after addingwater. After the photoplate was washed and dried, its reflectivity wasapproximately 35%. This reflective serpentine pattern of one micronlines and one micron spaces was of excellent image quality anddemonstrated the ability of this process to pre-record data and controlindicia having image sizes of one micron.

EXAMPLE 13

A commercially available Agfa-Gevaert Millimask HD photoplate having a4.5 micron thick emulsion and containing a screening dye was exposed toroom light for several minutes and then immersed for five minutes at 23°C. in a monobath developer having the following constituents: catechol,1/2 gram; sodium sulfite, 10 grams; sodium hydroxide, 2 grams; 58%solution of ammonium hydroxide, 50 milliliters; in a volume of one literafter adding water. After the photoplate was washed and dried, itsreflectivity was approximately 30%.

EXAMPLE 14

A commercially available Agfa-Gevaert Millimask HD photoplate having a4.5 micron thick emulsion and containing a screening dye was exposed toroom light for several minutes and then immersed for five minutes at 23°C. in a monobath developer having the following constituents:hydroquinone, 1/2 gram; sodium sulfite, 10 grams; sodium hydroxide, 2grams; 58% solution of ammonium hydroxide, 50 milliliters; in a volumeof one liter after adding water. After the photoplate was washed anddried, its reflectivity was approximately 25%.

The appearance of the surface of the finished recording medium varieswith the degree of reflectivity. At reflectivities of 50% or more it hasa silver-like appearance. In the 35% to 45% range its color is likewhite gold, and in the 17% to 30% range it looks like yellow gold. Belowabout 12% reflectivity it has a reflective black appearance similar toblack patent leather.

One of the principal differences between the single step diffusiontransfer process of the present invention and the prior art is that inthe present invention the unexposed and undeveloped silver halide is putinto solution quickly so that the silver ion complex forming reactiontakes place at a more rapid rate than silver diffusion transfer of theprior art since no chemical development is involved. In the prior artthe development of the negative black image must be essentiallycompleted before the remaining silver halide is complexed andtransferred; otherwise, the positive image would in essence be fogged.Thus, in the prior art a very high concentration of developing agent isused to rapidly complete the chemical development process, while in thepresent invention a low concentration of chemical developer is used.

Nothing limits the silver diffusion transfer process of the presentinvention to use as a data storage medium. The process may be used tomake other articles where high reflectivity is needed in conjunctionwith various types of information imaging.

In the broadest sense, the invention comprises dispersing highelectrical conductivity tiny metal spheres or spherical particles in adielectric medium of low thermal conductivity and low meltingtemperature to form a laser recording medium. If these small particlesare of very high volume concentration, e.g. between 20% to 70% of thevolume of the reflective surface layer, the medium can exhibit very highreflectivities in the visible spectrum even though the reflectivesurface would have no measurable electrical conductivity. Such adielectrically based electrically non-conducting reflective medium isdesirable for laser recording.

What is claimed is:
 1. A method of making a reflective laser recordingmedium from an unexposed photosensitive silver-halide emulsion layerincorporating a surface layer of high volume concentration silverprecipitating nuclei having a size primarily less than five hundredthsof a micron therein, the emulsion being disposed on a substrate with thenuclei layer disposed in said emulsion comprising,defining laserrecording area in the silver-halide emulsion, contacting the unexposedand undeveloped photosensitive silver-halide emulsion layerincorporating the surface layer of silver precipitating nuclei with anaqueous monobath comprising a weak silver-halide developing agent and arapid-acting silver-halide solvent for reacting with unexposed andundeveloped silver halide to form soluble silver ion complexes which aretransported by diffusion transfer to the silver precipitating nucleiwithin said emulsion layer where the silver of said silver ion complexesis precipitated and adsorbed on said nuclei in the presence of saiddeveloper acting as a reducing agent, to the extent that a layer ofaggregate and individual silver particles is formed exhibitingreflectivity of at least 15%.